Hinshelwood Kinetic Model Research Articles

Visible Light Induced Photocatalytic Degradation of Malachite Green by Solid State Synthesized MgFeO3–MgFe2MxO4 + δ (M = None, Mn4+, Ni2+, Zn2+, Eu3+, Dy3+, Yb3+) Nanocomposites

MgFe2O4 composite samples were synthesized by one-step solid state reactions between MgCl2 and FeCl3 at 600, 800 and 900 °C. The doped materials were synthesized using Ni(NO3)2, MnO2, Yb2O3, Zn(NO3)2 and Eu2O3dopant raw materials at 800 °C for 12 h. The obtained materials were characterized by powder X-ray diffraction technique. Rietveld analysis data showed that the obtained MgFe2O4 materials were crystallized in the cubic crystal system with the space group Fd-3m and lattice parameters a = b = c = 8.38 A. The morphologies of the synthesized materials were studied by field emission scanning electron microscope. The optical properties of the obtained materials showed that the materials had absorption in ultraviolet–visible light region. Direct optical band gap energies data of the obtained materials indicated that there are two band structure ranges. A strong band structure was in the range of 2.7 to 2.8 eV. The weak band structure was in the range of 1.8 to 2.0 eV. The photocatalytic performance of MgFe2O4 was also investigated for the degradation of Malachite Green (MG) in aqueous solution under direct visible light irradiation (Light power and colour: 40 W and white, respectively). The optimum conditions were obtained by design expert software for S3. It was found that the optimum conditions were 0.09 mL of H2O2, 28 mg of catalyst, and 40 min reaction time. The initial volume and concentration of MG solution were 60 mL and 70 ppm, respectively. It was found that MgFe2O4 had excellent efficiency under the optimized conditions at the presence of direct visible light irradiation. The degradation yield in the optimized conditions was 100%. According to the Langmuir–Hinshelwood (L–H) kinetic model, the kinetic degradation of MG followed a pseudo-first order kinetic model. The apparent rate constant (kapp) and correlation coefficient (R2) values were 0.1367 min−1 and 0.9225, respectively.

Electrochemical synthesis, photodegradation and antibacterial properties of PEG capped zinc oxide nanoparticles

The effect of surfactant and dopant on the properties of zinc oxide nanoparticles were studied by preparing polyethylene glycol (PEG) capped ZnO and tungsten doped PEG capped ZnO nanoparticles via the electrochemical method. These nanoparticles were characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet Diffuse Reflection Spectroscopy (UV-DRS), Scanning Electron Microscopy (SEM) and Electron Dispersive Analysis of X Rays (EDAX). The photocatalytic degradation of malachite green dye using these nanoparticles was studied under visible light. The effects of various reaction parameters like dye concentration, catalyst concentration, pH and time were studied to optimize the photodegradation reaction. Reusability of these nanoparticles was studied and no significant change was observed in the degradation efficiency of PEG capped ZnO till the fourth cycle, while there was a gradual decrease in the degradation efficiency of tungsten doped PEG capped ZnO. Langmuir- Hinshelwood kinetic model well describes the photodegradation capacity and the degradation of malachite green follows pseudo-first order kinetics.Photocatalytic studies reveal that PEG capping increases the degradation properties of ZnO while tungsten doping decreases the extent of PEG capping and has a detrimental effect on the degradation properties of ZnO. The prepared nanoparticles exhibit significant antibacterial properties against gram-positive Bacillus cereus and gram-negative Escherichia coli bacterial strains by agar well diffusion method.

Synergistic Effect of Maghemite and Titania Nanoparticles in PVA-Alginate Encapsulated Beads for Photocatalytic Reduction of Pb(II)

In this paper, maghemite (γ-Fe2O3) and titanium oxide (TiO2) nanoparticles were synthesized by hydrothermal and coprecipitation methods, respectively. These nanoparticles were combined together in various ratios (1:10, 1:20, 1:60, 1:80, and 1) and embedded in polyvinyl alcohol (PVA)-alginate beads. These beads were tested for photocatalytic behavior in eliminating toxic Pb(II) from the aqueous solution. The photocatalytic experiments were performed under sunlight irradiation and without sunlight. Several operating conditions such as initial Pb(II) concentration, pH, contact time, and TiO2: γ-Fe2O3 ratios were investigated to evaluate their effect on the process. The recycling attributes of these beads were also investigated. The results revealed that 100% of the Pb(II) was eliminated in 100 min at pH 7 under sunlight when the ratio of TiO2:γ-Fe2O3 was kept to 1. The PVA-alginate maghemite and titania beads showed better efficiency for Pb(II) removal than PVA-alginate titania beads and PVA-alginate maghemite beads. X-ray photoelectron spectroscopy (XPS) analysis also revealed that Pb(II) removal was via photocatalytic reduction due to the presence of Pb(0) in the high-resolution scan at 130–160 eV. Also, the PVA-alginate titania and maghemite beads can be readily isolated from the aqueous solution after the photocatalytic process and reused for at least 6 times without significant losses in their initial properties. The reduction of Pb(II) with PVA-alginate titania and maghemite beads fitted the Langmuir–Hinshelwood (L–H) kinetic model at a correlation coefficient (R2) of 0.9923.

Solar photocatalytic degradation of chlorophenols mixture (4-CP and 2,4-DCP): Mechanism and kinetic modelling

The solar-photocatalytic degradation mechanisms and kinetics of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) using TiO2 have been investigated both individually and combined. The individual solar-photocatalytic degradation of both phenolic compounds showed that the reaction rates follow pseudo–first-order reaction. During the individual photocatalytic degradation of both 4-CP and 2,4-DCP under the same condition of TiO2 (0.5 g L−1) and light intensities (1000 mW cm−2) different intermediates were detected, three compounds associated with 4-CP (hydroquinone (HQ), phenol (Ph) and 4-chlorocatechol (4-cCat)) and two compounds associated with 2,4-DCP (4-CP and Ph). The photocatalytic degradation of the combined mixture (4-CP and 2,4-DCP) was also investigated at the same conditions and different 2,4-DCP initial concentrations. The results showed that the degradation rate of 4-CP decreases when the 2,4-DCP concentration increases. Furthermore, the intermediates detected were similar to that found in the individual degradation but with high Ph concentration. Therefore, a possible reaction mechanism for degradation of this combined mixture was proposed. Moreover, a modified Langmuir–Hinshelwood (L-H) kinetic model considering all detected intermediates was developed. A good agreement between experimental and estimated results was achieved. This model can be useful for scaling-up purposes more accurately as its considering the intermediates formed, which has a significant effect on degrading the main pollutants (4-CP and 2,4-DCP).

Photocatalytic Degradation of Reactive Brilliant Red X-3B Based on Microwave Electrodeless Lamp and Long Lifetime Immobilized TiO<sub>2</sub>

A novel photocatalytic system (MEL/TiO2/QS) based on microwave electrodeless lamp (MEL) and TiO2 films supported on quartz sheets (TiO2/QS) was established for high photocatalytic efficiency and long catalyst life. The results showed that the degradation efficiency for reactive brilliant red X-3B in MEL/TiO2/QS was equally as that in a suspended TiO2 system. Furthermore, under the microwave irradiation, the TiO2/QS had high catalytic activity after successively used 10 times without additional separation and regeneration. The pseudo-first-order kinetics was employed to describe decomposition of the dye and reaction rates at different initial dye concentrations, followed by the Langmuir– Hinshelwood kinetic model. The mineralization process and final products were also analyzed by total organic carbon (TOC) and ion chromatography (IC). The research might be useful in the commercial scale application of low cost and high efficiency photocatalytic process. Keywords: Catalyst regeneration, microwave electrodeless lamp, reactive brilliant red X-3B, TiO2 films.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

Thermodynamic Equilibrium and Reaction Kinetics for the Esterification of Lactic Acid with Ethanol Catalyzed by Acid Ion-Exchange Resin

The heterogeneous catalysis of lactic acid (88 wt %) esterification with ethanol in the presence of Amberlyst 15-wet was studied for catalyst loading of 1.2−3.9 wt %, initial molar ratio of reactants of 1.1−2.8, and temperature from 50 to 90 °C. In this work a methodology based on the UNIQUAC model was developed to determine the thermodynamic equilibrium constant since in the literature there is inconsistency concerning the temperature dependence of the thermodynamic equilibrium constant. A simplified Langmuir−Hinshelwood kinetic model was used to predict the experimental data. The proposed rate law is r = kc(aEthaLa − aELaW/K)/(1 + KEthaEth + KWaW)2; the kinetic parameters are the preexponential factor, kc,0 = 2.70 × 107 mol·g-1·min-1, and the activation energy, Ea = 49.98 kJ/mol. The equilibrium reaction constant is K = 19.35 exp(−515.13/T (K)) with reaction enthalpy 4.28 kJ/mol. The model reasonably predicts the kinetic experimental data, and it will be very useful to apply to the design and optimizati...

Direct Experimental Evidence for a Heterogeneous Reaction of Ozone with Bromide at the Air−Aqueous Interface

Recent experimental and theoretical evidence has indicated an enhancement of the heavier halide ions at the air-aqueous interface, relative to their bulk concentrations. This, along with an order of magnitude discrepancy between measured and predicted Br2 production in the reaction of ozone with deliquesced NaBr aerosol, has led to the suggestion that an interface reaction occurs between ozone and bromide. We have used harmine, a beta-carboline alkaloid, as an interface-sensitive fluorescent pH probe in order to measure pH changes associated with the interfacial reaction of ozone and bromide. The rate of pH change depends upon the bulk bromide concentration in a way which is well described by a Langmuir-Hinshelwood kinetic model. In the presence of octanol at the interface, the rate of pH change tracks the octanol adsorption isotherm, as expected if octanol enhances the concentration of ozone at the surface.

Adsorption and Photocatalyzed Oxidation of Methylated Arsenic Species in TiO2 Suspensions

Monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) are used as herbicides in the agriculture industry. We have demonstrated that MMA and DMA are readily degraded upon TiO2 photocatalysis. DMA is oxidized to MMA as the primary oxidation product, which is subsequently oxidized to inorganic arsenate, As(V). The adsorption of MMA and DMA on Ti02 surface was measured as a function of initial arsenic concentration and solution pH. The pH of the solution influences the adsorption and photocatalytic degradation to a similar degree, due to the speciation of the arsenic substrates and surface charge of TiO2 as a function of pH. The mineralization of MMA and DMA by TiO2 photocatalysis follows the Langmuir-Hinshelwood kinetic model. Addition of tert-butyl alcohol, a hydroxyl radical scavenger, during TiO2 photocatalysis dramatically reduces the rate of degradation, indicating that *OH is the primary oxidant. For dilute solutions, TiO2 may also be applicable as an absorbent for direct removal of a variety of arsenic species, namely As(III), As(V), MMA, and DMA, all of which are strongly adsorbed, thus eliminating the need for a multistep treatment process.

Photocatalytic Degradation of Rhodamine Dyes with Nano-TiO2

The photocatalytic degradation of various Rhodamine dyes with different functional groups, namely, Rhodamine B (C28H31ClN2O3), Rhodamine 6G (C28H31ClN2O3), Rhodamine Blue (C28H32N2O3), and Rhodamine 6G perchlorate (C28H31ClN2O7) was investigated under UV irradiation. The kinetics of degradation was determined in the presence of two catalysts: commercial Degussa P-25 and TiO2 synthesized by the combustion solution method. The effect of organic solvents (ethanol and acetonitrile) and metal ions (Cu2+, Fe3+, Zn2+, and Al3+) on the photodegradation of Rhodamine B was investigated. The presence of solvents and metal ions significantly reduced the degradation rate. A detailed Langmuir−Hinshelwood kinetic model was developed to explain the effect of Cu2+ on the rate of photodegradation. It was shown that the degradation rate reduces primarily because of a decrease in electron concentration.